Delay generator having first and second resonant circuits controlling delay intervaland pulse duration respectively



June 2, 1964 M. FISCHMAN 3,135,877

DELAY GENERATOR HAVING FIRST AND SECOND RESONANT CIRCUITS CONTROLLING DELAY INTERVAL AND PULSE DURATION RESPECTIVELY 2 Sheets-Sheet 1 Filed March 1, 1962 26 I :4 10 I2 18 l6 1 r i T 78F 2O 92 (/VBZ VB'R: l CT I 66:OUTPUT 44 V1" 32 g 1 \BISTABLE I v J INPUT (R V K48 K34 Y l A VQ2 BISTABLE M v V 62/ so 46 0/ T2 e 74 7s 76 /\/T2 1's 4 V INVERTER 72 INVENTOR. MARTIN FISCHMAN BY ATTORNEY June 2, 1964 DURATION RESPECTIVELY Filed March 1, 1962 M. FISCHMAN DELAY GENERATOR HAVING FIRST AND SECOND RESONANT CIRCUITS CONTROLLING DELAY INTERVAL AND PULSE 2 Sheets-Sheet 2 (J INVENTOR. MARTIN FISCHMAN AT TORNE Y United States Patent 3,135,877 DELAY onnnunron uavnvo FIRST AND suc- OND RESGNANT CRiIUTTS CGNTRGLLING ELAY INTERVAL AND PULSE DURATIGN RESPECIWELY Martin Fischman, Wantagh, N.Y., assignor to General Telephone and Electronics Laboratories, line, a corporation of Delaware Filed Mar. 1, 1962, Ser. No. 176,748 8 Claims. (Cl. 39788.5)

This invention relates to delay generators.

In many electronic systems, the time interval between two events must be precisely controlled. In a typical application, a voltage pulse corresponding to the first event is coupled to the input of a delay generator and, after a predetermined interval has elapsed, an output pulse corresponding to the second event is produced at the output of .the generator. It is highly desirable that such delay generators be extremely stable as well as capable of providing precisely controlled delays.

Accordingly, it is an object of my invention to provide an improved delay generator.

Another object of the invention is to provide a delay generator which is stable, precise, and provides delays which are practically independent of variations in supply voltage and transistor parameters.

Still another object is to provide a delay generator which may be rapidly reset and hence will respond to signals having high repetition rates.

A further object is to provide a delay generator in which the delay may be accurately and easily adjusted between relatively wide limits.

-Yet another object is to provide a delay generator in which the ratio of the delay interval to the recovery period is high.

In the present invention, a delay generator is provided in which the delay interval is precisely controlled by a first resonant circuit comprising an initially charged capacitor and a first inductor. The duration of the output pulse is controlled by a second resonant circuit comprising the capacitor and a second inductor.

The first inductor is connected in series with the charged capacitor upon application of an input signal to the generator. This results in a halt cycle of sinusoidal current flow through the capacitor at a frequency equal to the resonant frequency of the first resonant circuit. When the current through the capacitor is reduced to zero at the end of the half cycle, switching circuits initiate an output pulse while simultaneously disconnecting the first inductor from the circuit and coupling the second inductor in series with the capacitor. As a result, a sinusoidal current having a frequency equal to the resonant frequency of the second resonant circuit flows through the capacitor and the second inductor. When this current goes to zero, the output pulse is terminated by the switching circuits and the second inductor is disconnected from the circuit. Thus, the first and second resonant circuits control the delay interval and the duration of the output pulse respectively.

In one embodiment of the invention, first, second and third series circuits are provided. The first series circuit comprises the first inductor and a first inductor switch, the second series circuit includes the second inductor and a second inductor switch, and the third series input circuit comprises the capacitor. The three series circuits are connected in parallel.

The first inductor switch is coupled to and controlled by the output of a first bistable switching circuit of a type designed to generate an output pulse when a suitable input signal is applied to a first of its two input terminals and which terminates the output pulse when a suitable signal is applied to its second input terminal. Similarly, the second inductor switch is coupled to, and controlled by, the output of a similar second bistable switching circuit. First and second pulse forming circuits responsive to the current through the capacitor are also provided, the output of the first pulse forming circuit being coupled to the first input of the second bistable switching circuit and the output of the second pulse forming circuit being coupled to the second inputs of the first and second bistable switching circuits.

When an input pulse is applied to the first input terminal of the first bistable switching circuit, the first inductor switch is closed and a sinusoidal current, having a frequency equal to the resonant frequency of the first inductor and the capacitor, triggers the first pulse forming circuit. After a half cycle, the current drops to zero and the first pulse forming circuit applies a pulse to the second bistable switching circuit thereby closing the second inductor switch and producing the delay generator output pulse at the output of the second bistable switching circuit. As the capacitor current reverses direction, it triggers the second pulse forming circuit thereby applying a pulse to the first bistable switching circuit opening the first inductor switch.

During the second half cycle, the frequency of the sinusoidal capacitor current is equal to the resonant frequency of the second inductor and the capacitor. When this current goes to zero, the second pulse forming circuit applies a pulse to the second bistable switching circuit thereby opening the second inductor switch and terminating the output pulse.

The above objects of and the brief introduction to the present invention will be more fully understood and further objects and advantages will become apparent from a study of the following description in connection with the drawings, wherein:

FIG. 1 is a schematic diagram of our delay generator, and

FIG. 2 depicts idealized waveforms of the currents and voltages produced in the delay generator of FIG. 1.

Referring to FIG. 1, there is shown a schematic diagram or my delay generator in which first and second variable inductors 1t and 12 are connected in series with first and second inductor switches 14 and 16 respectively. Switch 14 comprises a type NPN transistor having its emitter electrode grounded and its collector electrode connected to inductor 10. Switch 16, which is a type PNP transistor, has its emitter grounded and its collector connected through diode 18 to inductor 12. A capacitor 20, having one end connected to ground through an impedance element or resistor 22 and its other end connected to the junction of inductors 16 and 12, is arranged to be switched in series with either inductor 10 or inductor 12 by switches 14 and 16 respectively to obtain first and second resonant circuits. A D.-C. power source 24 having a magnitude E is coupled through a resistor 26 to the junction of inductors 1t and 12 and capacitor 20.

A bistable multivibrator 39, having first and second input terminals 32 and 34 respectively, has its output terminal 36 connected to the base of transistor 14. Multivibrator 30, which may be of any known suitable type such as that illustrated in Fig. 198, page 203 of the Department of the Army Technical Manual TM 11-690, Basic Theory and Application of Transistors, March 1959, generatesa pulse V at output terminal 36 when a negative input pulse V is applied to terminal 32. These voltage pulses are illustrated in FIGS. 2b and 2a respectively. When a negative going pulse is applied to terminal 34- of multivibrator St), the pulse V at terminal 36 is terminated. (It shall be understood that when reference is made to the voltage at a terminal or other portion of the circuit, the voltage referred to is measured between the designated point and ground.)

.FIG. 2i. and 76 and the input resistances of multivibrator 3i and 7 tion opposing the arrow in FIG. 1.

Eat a time t il, a negative pulse V (see FIG. 2a) is applied to terminal 320i multivibrator 36, a positive pulse V (FIG; 2b) is applied to the base of type NPN transistor 14 causing it to conduct. Capacitor which has been charged to a voltage +E by voltage source 24 then begins to discharge through inductor 1%, the emitter-collector path of transistor 14 and the emitter-base path of a type PNP transistor 49. (Initially, current will flow from ground through resistor 22 driving the base of transistor 49 negative with respect to its emitter causing it to conduct. However, the time required to drive transistor 4% into conduction is so short and the resistance of the baseemitter path of transistor 40 is so low when compared to the value of resistor 22, that the current through resistor 22is very small. This is indicated by FIG. 2e which depicts the voltage V across resistor 22.)

The collector of transistor 4% is connected to a negative D.-C, voltage source 42 through a resistor 44 and is coupled to input terminal 46 of bistable multivibrator 48 through a capacitor 50. A positive voltage pulse V (FIG. 2;) is produced at the collector of transistor 45. and is diilerentiated by capacitor 53 and the input resistance of multivibrator 43 resulting in alternate positive and negative voltage spikes V as shown in FIG. 2g. Multivibrator 43 is identical to multivibrator 3E and therefore it responds only to negative pulses applied to input terminal 46. Thus, the positive spike occurring at 1:0 in the voltage V- has no effect on multivibrator 48, the voltage at output terminal 52 being zero during the interval in which transistor 4%} is conducting.

The current i through capacitor 2! changes sinusoidally during the interval between t=tl and t=T as indicated by the solid curve 66a of FIG. 2d, while the voltage across the capacitor V (FIG. 2c) changes sinusoidally to a value -E. The duration of the delay interval between t-ll and t=T is equal to m/L -C, where L is the inductance of the first inductor in henries and C is the capacitance of capacitor 2% in far-ads. As the current i changes direction at t=T transistor 4% is cut ofifand type NPN I transistor 62 begins conducting. When transistor 40 ceases to conduct, the drop in the collector voltage V is differentiated producing a negative spike 64 in V driving'multivibrator 48 into a conducting state and producing an output pulse V across output terminals 66.

' Pulse V also drives transistor '16 into conduction connecting inductor 12 in series with capacitor 29.

The collector electrode of transistor 62 is biased by a positive D.-C. voltage source 76 through a resistor 71.

' When transistor 62 is driven into conduction, its collector is driven negative resulting in the voltage V shown in This voltage is difierentiated by capacitors 72 inverter '78 and, as a result, a negative spike V (FIG. 2 is applied to input terminal 34 of multivibrator 39. Negative spike V cuts off multivibrator 3t) and drives transistor 14 out of conduction efiectively' disconnecting inductor 145 from the circuit. A spike is also applied to input terminal 74' of multivibrator 48 through capacitor 76 and inverter 78. However, due to the polarity reversal occurring in inverter 78, the spike applied to terminal 74 of multivibrator 48 is positive and the multivibrator remains conducting. V I

Since the delay period T is determined by the current z through the high Q resonant circuit comprising capacitor 2i) and inductor 14 the delay is extremely stable and relatively unafiected by changes in the supply voltage E or variations in the characteristics of the transistor. This is shown in curves 60b and 6430 (FIG. 2d) which show the capacitor currents i for higher and lower than normal supply voltages B respectively.

During the recovery period between t=T and t=T, the capacitor current i is sinusoidal and flows in a direc- The capacitor voltage V (FIG. 2c) changes sinusoidally from E to '+E during this period as shown in FIG. 2 c, rectifier l8 preventing 4., current flow in the direction from inductor 12 to transistor 16 during the portion of the recovery period when V 'is positive. The duration of the recovery period between t=T and 1:! is equal to fl'\/L2C, where L is the inductance of the second inductor l2. At the end of the re-.

covery period at time i=T, the capacitor current 2' goes to zero and transistor 62 becomes non-conducting. The

increase in collector voltage V (FIG. 2;) is difierentiated producing a positive spike V at the input of inverter 78. This spike, after inversion, is applied to input terminal 74 of multivibrator 48 cutting it oh? and reducing the voltage V across output terminal66 to zero. When voltage V goes to zero, transistor 16 is cut off restoring the delay generator to its initial condition. A.

new input pulse may now be applied to terminal 32 of multivibrator 39 and the cycle repeated.

The duration of the output pulse V is precisely de- 7 termined by the resonant frequency of capacitor 20 and second inductor l2 and is relatively independent of changes insupply voltage E. This is shownby the solid curve 6th! for a normal voltage supply and curves 602 and 69 for above andbelow normal supply voltages respectively. V

In a typical embodiment of my invention the component and voltage values are as follows:

With these parameters, delays of approximately 10 microseconds and pulse durations of approximately 1 nucrosecond may be obtained. The delays and durations may be varied over wide limits by suitable choice of the inductive and capacitive elements. The delay period remains within 1.1 percent as the supply voltage 24 is varied from 5 to 15 volts.

As many changes could be made in the above construe tion and many different embodiments could be made without departing from the scope thereof it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A delay generator'com'prising (a) first, second, and third series circuits, said first series circuit including a first inductor and a first inductor switching means, said second series circuit including a second inductor and a second inductor switching means, and said third series circuit including a capacitor, said first, second, and third series circuits being connected in parallel,

(b) first and second bistable switching means each having an output terminal and first and second input terminals, the output terminals of said first and .sec-

ond bistable switching means being coupled to the rst and second inductor switching means respec-' bistable switching means, an output pulse being produced at the output terminal of said second bistable switching means a predetermined interval after application of an input pulse to the first inputterminal of said first bistable switching means, said predetermined interval being determined by the resonant fre quency of said capacitor and said first inductor.

2. A delay generator comprising 6 resistor, said first, second and third series circuits being connected in parallel, (d) first and second bistable multivibrators each having an output terminal and first and second input (a) first, second, and third series circuits, said first 5 terminals, the output terminals of said first and secseries circuit including a first inductor and a first 0nd bistable multivibrators being coupled to the secinductor switching means, said second series circuit 0nd electrodes of said first and second transistors including a second inductor and a second inductor respectively, and switching means, and said third series circuit includ- (e) first and second pulse forming means each having ing a capacitor and an impedance element, said first, 10 an input and an output, the inputs of said first and second, and third series circuits being connected in second pulse forming means being coupled to the parallel, junction of said capacitor and said resistor, the out- (b) first and second bistable switching means each havput of said first pulse forming means being coupled ing an output terminal and first and second input terto the first input of said second bistable multivibraminals, the output terminals of said first and second 5 tor, and the output of said second pulse forming bistable switching means being coupled to the first means being coupled to the second inputs of said and second inductor switching means respectively, first and second bistable multivibrators, an output and pulse being produced at the output terminal of said (0) first and second pulse forming means each having second bistable multivibrator a predetermined inan input and an output, the inputs of said first and terval after application of an input pulse to the first second pulse forming means being coupled to the input terminal of said first bistable multivibrator, said junction of said capacitor and said impedance elepredetermined interval being determined by the resoment, the output of said first pulse forming means nant frequency of said capacitor and said first inbeing coupled to the first input of said second bistable ductor. switching means, and the output of said second pulse 5. The delay generator defined by claim 4 wherein f r g means being coupled to the second inputs said first transistor is a type NPN and said second tranof said first and second bistable switching means, an sistor is a type PNP, the first, second and third electrodes output pulse being produced at the output terminal of said first and second transistor corresponding to emitof said second bistable switching means a predeterter, base and collector electrodes respectively. mined interval after application of an input pulse to 6, A d l generator comprising the first input terminal Of said first bistable switching (a) a first series circuit including a first inductor and means, said predetermined interval being deiefminsd a first transistor having first, second, and third elecb the resonant frequency of said capacitor and said trodes, said first inductor being coupled in series with first inductor. the first and third electrodes of said first transistor,

3. A delay generator comprising (b) a second series circuit including a second inductor first, second, and third eries Circuits, aid fi st and a second transistor having first, second, and third Series Circuit iflduding a 55st inductor and a s electrodes, said second inductor being coupled in inductor switching means, said second series circuit Series ith th fi t d thi d electrodes f id including a second inductor and a second inductor d t i t switching means, and said third series circuit iIlClLl(l (c) a third series circuit including a capacitgr and a ing a capacitor and a resistor, said first, second, and resistor, said first, second and third series circuits third series circuits being connected in parallel, b i Connected i ll l,

( first and seCOHd ble multivibrators (d) first and second bistable multivibrators each having an ouiPut terminal and rst a d second 1I1Pl1t ing an output terminal and first and second input terterminals, the output terminals, of said first and minals, the output terminals of said first and second second bistable multiV being coupled to j bistable multivibrators being coupled to the second first and second ind switching means Tespsctlveelectrodes of said first and second transistors respecl nd tively, and

( first and second Pulse forming means each hill/111g (e) third and fourth transistors each having first, secan input and an output, the inputs of said first and 0nd, and third electrodes, the first and second elecsecond Pulse forming means being coupled {0 tbs trodes of said third and fourth transistors being junction of said capacitor and said resistor, this coupled across said resistor, the third electrode of put of said first pulse forming means being coupled said third transistor being coupled to the first input to the first input of said second bistable multivibrator, of said second bistable multivibrator and the third and the output of said second pulse forming means electrode of said fourth transistor being coupled to being coupled to the second inputs of said first and the second inputs of said first and second bistable second bistable multivibrators, an output pulse being muliivibfatofs, 011tP11t Pulse b61115 P f produced at the output terminal of said second bithe p t i m all of said second bistable multivistable multivibrator a predetermined interval after i a Predetennmed mien/a1 flfte? PP of application of an input pulse to the first input terrni- Input P F the first p terminal of 5 first nal of said first bistable multivibrator, said predeterg fflblg tmultivrgrggprghoplgeldtegzfigggy rggegill a etng e ermine e mmed mterva-l bemg d-etvmmed gl zf i capacitor and said first inductor and the duration of quency of said capacitor-zinc Sal SL m c o said output pulse being determined by the resonant A delay gerieratcir p i P d frequency of said capacitor and said second inductor.

(a) a first ser es ClI'CllllZ including a first inductor an 7 A delay generator comprising a first traPslstor havlng Second i i i (a) a first series circuit including a first inductor and trodes, said first inductor being coupled in seneswith a first transistor having first, second, and third e1ec the first and flqlrd F P'Q said first trfinslstor trodes, said first inductor being coupled in series with a Second Senes clrcmt mdudmg a Second inductor the first and third electrodes of said first transistor, and a Second transistor having first, second, and (b) a second series circuit including a second inductor t d electrodes, said second iflducto?" being pled and a second transistor having first, second, and third in series with the first and th rd e ect od o said electrodes, said second inductor being coupled in second transistor, series with the first and third electrodes of said sec- (c) a third series circuit including a capacitor and a 0nd transistor,

' (c) a third series circuit including a capacitor and a resistor, said first, second and third series circuits being connected in parallel,

(d) first and second bistable multivibrators each having an output terminal and first and second input terminals, the output terminals, of said first and second bistable multivibrators being coupled to the second electrode of said first and second transistors respectively,

(e) third and fourth transistors each having first, second, and third electrodes, the first and second electrodes of said third and fourth transistors being coupled across said resistor, and

(f) first and second difierentiating means, said first ditferentiating means coupling the third electrode of said third transistor to the first input of said second bistable multivibrator and said second difierentiating means coupling the third electrode of said fourth transistor to the second inputs of said first and second bistable multivib'rators, an output pulse being pro- 20 duced at the output terminal of said second bistable multivibrator a predetermined interval after applicafirst and third transistors are type NPN and said second and fourth transistors are type PNP, the first, second and third electrodes of said first, second, third and fourth transistors corresponding to the emitter, base and collec- 15 tor electrodes respectively.

Curtis Aug '12, 1958 l 

1. A DELAY GENERATOR COMPRISING (A) FIRST, SECOND, AND THIRD SERIES CIRCUITS, SAID FIRST SERIES CIRCUIT INCLUDING A FIRST INDUCTOR AND A FIRST INDUCTOR SWITCHING MEANS, SAID SECOND SERIES CIRCUIT INCLUDING A SECOND INDUCTOR AND A SECOND INDUCTOR SWITCHING MEANS, AND SAID THIRD SERIES CIRCUIT INCLUDING A CAPACITOR, SAID FIRST, SECOND, AND THIRD SERIES CIRCUITS BEING CONNECTED IN PARALLEL, (B) FIRST AND SECOND BISTABLE SWITCHING MEANS EACH HAVING AN OUTPUT TERMINAL AND FIRST AND SECOND INPUT TERMINALS, THE OUTPUT TERMINALS OF SAID FIRST AND SECOND BISTABLE SWITCHING MEANS BEING COUPLED TO THE FIRST AND SECOND INDUCTOR SWITCHING MEANS RESPECTIVELY, AND (C) FIRST AND SECOND PULSES FORMING MEANS, SAID FIRST AND SECOND PULSE FORMING MEANS BEING RESPONSIVE TO THE CURRENT THROUGH SAID CAPACITOR, THE OUTPUT OF SAID FIRST PULSE FORMING MEANS BEING COUPLED TO THE FIRST INPUT OF SAID SECOND BISTABLE SWITCHING MEANS, AND THE OUTPUT OF SAID SECOND BISTABLE SWITCHING MEANS, AND THE OUTPUT OF SAID SECOND PULSE FORMING MEANS BEING COUPLED TO THE SECOND INPUTS OF SAID FIRST AND SECOND BISTABLE SWITCHING MEANS, AN OUTPUT PULSE BEING PRODUCED AT THE OUTPUT TERMINAL OF SAID SECOND BISTABLE SWITCHING MEANS A PREDETERMINED INTERVAL AFTER APPLICATION OF AN INPUT PULSE TO THE FIRST INPUT TERMINAL OF SAID FIRST BISTABLE SWITCHING MEANS, SAID PREDETERMINED INTERVAL BEING DETERMINED BY THE RESONANT FREQUENCY OF SAID CAPACITOR AND SAID FIRST INDUCTOR. 